Extract

Introduction. With the progress of petrographical research, spherulitic rocks of basic composition are now known to have a fairly wide distribution in the British Isles. Examples have been described by Cole1 and Sollas,2 from Ireland; by Groom,3 from the Lake District; and by Blake4 and Cole,5 from Anglesey, to mention only a few occurrences. Scottish examples were first described by Clough and Harker6 from the Tertiary igneous rocks of Skye, although Judd and Cole7 many years previously had described altered spherulitic tachylytes or basalt glasses, which now perhaps would be called variolites. Variolites have now been discovered at several localities in the West of Scotland, notably at Ardmucknish,8 Loch Melfort, and Easdale, in Argyllshire.9 In Cowal Mr. Clough has described spherulitic rocks, provisionally designated as trachytes,10 but which, from examination of slides kindly lent by the Geological Survey, may be considered as belonging to the sub-acid glasses and the less basic tachylytes. The latter correspond well with the variolite of Upper Loch Fyne.

Upper Loch Fyne.Field Occurrence.—Large boulders of a variolitic basalt were first discovered on Upper Loch Fyne by the Geology Class of Glasgow University during a week-end visit to Inveraray in February, 1912. Many of these boulders, which were practically unworn, were about 12 inches in width, with varying lengths. The margins showed compact greyish-blue non-spherulitic rock, which continued inwards to a depth of 1 inch. Then came variolitic bands on each side about 1 inch in width. The interior

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